Recently, cells being small-size and light-weight and having a long service life and a high energy density are demanded as a power source for small-size electron devices with the rapid advance of the electronics. The non-aqueous electrolyte cells containing lithium as a negative electrode active substance have been known as one of the cells having a high energy density because an electrode potential of lithium is lowest among metals and an electric capacity per unit volume is large. Many kinds of them are actively studied irrespectively of primary cell and secondary cell, a part of which is put into practical use and supplied to markets. For example, the non-aqueous electrolyte primary cells are used as a power source for camera, electron watch and various memory backups, while the non-aqueous electrolyte secondary cells are used as a driving power source for note-type personal computer, mobile-phones and the like.
At the present days, a porous film of a polyolefin such as polyethylene, polypropylene or the like is used in a separator arranged between a positive electrode and a negative electrode in these non-aqueous electrolyte cells for preventing the short-circuiting between the positive and negative electrodes. In the separator are formed many pores for passing ion in the charge and discharge of the cell, so that the passing of the ion is not obstructed under the usual use environment.
In the non-aqueous electrolyte cell, lithium as a negative electrode active substance violently reacts with a compound having an active proton such as water, alcohol or the like, so that a combustible aprotic organic solvent is used in the electrolyte of the cell. However, the aprotic organic solvent has a drawback that a risk of fire-ignition is high. For this end, the separator for the non-aqueous electrolyte cell has a function that when the temperature in the cell rises to 130-150° C. or more due to the flowing of an abnormal current based on accidental short-circuiting or the like, the pores in the separator are closed by fusing the separator itself to prevent the passing of the ion between the positive and negative electrodes or shut off the current to stop the rise of the temperature (shut-down effect), which reduces the risk of firing and igniting the aprotic organic solvent in the electrolyte (see JP-A-8-138644).